Stiffening assembly

ABSTRACT

A stiffenable structure is made of longitudinal beams that are positioned around a longitudinal axis. In one state, the longitudinal beams are bendable so that the structure is bendable. As the structure bends, the longitudinal beams slide longitudinally with reference to one another. In a second state, the beams are clamped in a fixed position relative to one another so that the structure is stiffened. In some aspects the longitudinal beams are made of two or more longitudinal laminar elements. As each beam bends, the laminar elements slide longitudinally with reference to one another. Each beam, and accordingly the structure, is stiffened by preventing the laminar elements from sliding longitudinally relative to one another.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/127,143, filed May 27, 2008 and entitled “Stiffening Assembly,” whichis incorporated by reference herein, in its entirety.

BACKGROUND

1. Field of Invention

This invention relates to devices that may be varied between bendableand stiffened states, and more particularly to such stiffenableassemblies in tubular arrangements in devices for minimally invasivesurgery.

2. Art

Minimally invasive surgical tools, such as those used for laparoscopicsurgery, are often substantially rigid. Consequently, their reach islimited. To achieve useful triangulation of instruments at an internalsurgical site, instruments must be inserted through multiple ports inthe patient's body wall.

Flexible endoscopes that allow passage of two or more instruments to aninternal surgical site are being used for surgery because such userequires only a single entry port into the body. But endoscopestypically lack rigidity and lack instrument triangulation at the distalend of the endoscope. Since the surgical instruments experience reactiveforces from tissue (e.g., when retracting, suturing, etc.), someendoscopes rely on bracing against surrounding tissue to provide astable base for the instruments. Other endoscopes rely on astiffening/rigidizing mechanism. For instance, cables used to steer theendoscope may be locked in position or tensioned to increase friction inthe endoscope's joints in order to stiffen the endoscope. Butsurrounding tissue used for bracing may be soft, and small controlcables are subject to stretching due to the moment loads at theendoscope's distal end. Accordingly the flexible endoscope may only bemade a limited amount more stiff than its flexible state. In addition,longitudinal tension on control cables used to increase friction betweenan endoscope's joints may cause the distal tip of the endoscope to move.

What is desired, therefore, is a structure that is significantly stifferin a rigid state than in a flexible state. It is further desired thatthe structure be rigidizable in various shapes—bent or straight—and thatsuch rigidizing does not affect the shape.

SUMMARY

A stiffenable structure is made of longitudinal beams that arepositioned around a longitudinal axis to form a tube. The longitudinalbeams are bendable, and in one state the beams are able to slidelongitudinally relative to one another so that the structure isbendable. In a second state, the longitudinal beams are clamped in afixed position relative to one another so that the structure isstiffened in a desired two- or three-dimensional curved shape. In someaspects the stiffenable structure is positioned around a guide thatdirects one or more minimally invasive surgical instruments to asurgical site. The guide may be an endoscope or other flexiblestructure, which may be steerable.

The longitudinal beams may be clamped in a fixed position in variousways, including the use of vacuum, so that ambient pressure compressesthe beams, and the use of various mechanical clamping implementations,such as by cable tension or by the use of an expandable material. Thebeams may be clamped in a fixed position relative to one another byclamping them against one another or by clamping them to an intermediatestructure, such as a bulkhead.

In some aspects the longitudinal beams are made of two or morelongitudinal laminar elements. As each beam bends, the laminar elementsslide longitudinally with reference to one another. Each beam isstiffened by clamping the laminar elements against one another.

Aspects of the invention may be used for minimally invasive surgicaldevices, such as surgical instrument guide tubes. Stiffening the distalend of a guide tube creates a stable platform to counteract reactiveforces on surgical instruments during surgery, thus allowing a surgeonto effectively perform surgical tasks such as suturing and repeatedlygrasping, pulling, and releasing tissue.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic perspective view that illustrates a generalconfiguration of an aspect of the invention.

FIGS. 2A and 2B are diagrammatic plan views of longitudinal beamsbending and sliding with reference to one another as a guide bends alongits longitudinal axis.

FIG. 3 is an exploded perspective diagrammatic view of bendablelongitudinal beams in a stiffening mechanism.

FIGS. 4A-4F are diagrammatic cross-sectional end views that illustratevarious cross sectional shapes of longitudinal beams and arrangements ofthe beams around a longitudinal axis.

FIGS. 5A-5C are diagrammatic cross-sectional end views of variouslaminar longitudinal beams.

FIGS. 6A-6D are diagrammatic side views of various illustrative laminarlongitudinal beam configurations.

FIG. 7A is a diagrammatic cross-sectional view that shows longitudinalbeams arranged in a stiffening assembly around a longitudinal axis, andthe longitudinal beams are positioned between an inner wall and an outerwall. FIGS. 7B and 7C are details of another implementation of theclamping state details shown in the FIG. 7A illustration. FIGS. 7D and7E illustrate two clamping states of FIG. 7A.

FIG. 8 is a schematic view of a vacuum clamping system for a minimallyinvasive surgical assembly.

FIG. 9 is a diagrammatic perspective view of another aspect of astiffenable assembly in which intermediate structures (e.g., bulkheads)are used.

FIGS. 10A-10D are diagrammatic cross-sectional views that illustratevarious aspects and implementations of clamping mechanisms.

FIG. 11 is a diagrammatic view that illustrates another implementationof a stiffening assembly positioned around a distal portion of asteerable, bendable guide.

DETAILED DESCRIPTION

This description and the accompanying drawings that illustrate aspectsand embodiments of the present invention should not be taken aslimiting—the claims define the protected invention. Various mechanical,compositional, structural, electrical, and operational changes may bemade without departing from the spirit and scope of this description andthe claims. In some instances, well-known circuits, structures, andtechniques have not been shown or described in detail in order not toobscure the invention. Like numbers in two or more figures represent thesame or similar elements.

Further, this description's terminology is not intended to limit theinvention. For example, spatially relative terms—such as “beneath”,“below”, “lower”, “above”, “upper”, “proximal”, “distal”, and thelike—may be used to describe one element's or feature's relationship toanother element or feature as illustrated in the figures. Thesespatially relative terms are intended to encompass different positionsand orientations of the device in use or operation in addition to theposition and orientation shown in the figures. For example, if thedevice in the figures is turned over, elements described as “below” or“beneath” other elements or features would then be “above” or “over” theother elements or features. Thus, the exemplary term “below” canencompass both positions and orientations of above and below. The devicemay be otherwise oriented (rotated 90 degrees or at other orientations)and the spatially relative descriptors used herein interpretedaccordingly. Likewise, descriptions of movement along and around variousaxes includes various special device positions and orientations. Inaddition, the singular forms “a”, “an”, and “the” are intended toinclude the plural forms as well, unless the context indicatesotherwise. And, the terms “comprises”, “comprising”, “includes”, and thelike specify the presence of stated features, steps, operations,elements, and/or components but do not preclude the presence or additionof one or more other features, steps, operations, elements, components,and/or groups. Components described as coupled may be electrically ormechanically directly coupled, or they may be indirectly coupled via oneor more intermediate components.

A. Stiffening

FIG. 1 is a diagrammatic perspective view that illustrates a generalconfiguration of an aspect of the invention. FIG. 1 shows a flexibleguide 2 having a proximal end 4 and a distal end 6. A longitudinal axis8 is defined between the proximal and distal ends. Guide 2 is depictedas having at least one longitudinal channel 10 that extends from theproximal end (or nearly so) to the distal end (or nearly so). The singlechannel 10 shown in FIG. 1 is illustrative of one or more channels,which may be of various and differing diameters. Such channels may beused for, e.g., introducing surgical tools and equipment (e.g., surgicalinstruments, needle and suture, and the like) to a surgical site,introducing fluid (gas, liquid) to the surgical site, or removing matterfrom the surgical site (e.g., using suction, biopsy sampling, and thelike).

In one aspect, guide tube 2 is an endoscope. Accordingly, guide 2 isdepicted in FIG. 1 as including an illustrative distal end stereoscopicvision system 12. Vision system 12 is illustrative of various endoscopicvision systems that may be used, including direct viewing opticalsystems and electronic imaging systems with image capture components ateither the proximal and distal ends. Vision systems may be mono- orstereoscopic. Steerable, flexible endoscopes are known and may besupplied by, e.g., Olympus Corporation (JP), Karl Storz GmbH & Co. KG(DE), or other vendors.

Guide 2 need not be an endoscope, however, and may be any flexibledevice that helps guide another device (e.g., a minimally invasivesurgical instrument having an outer diameter of approximately, e.g., 2mm, 5 mm, 8 mm, and similar sizes) from the proximal end to the distalend. Further, some or all of guide 2 may be steerable. For example, insome cases only the distal end is actively steerable, although theentire length of guide 2 may be flexible. In other cases the entirelength of guide 2 may be steerable. In all cases, the lengths of thesteerable sections in the guide may differ from one another.Illustrative steering mechanisms include manually or servomotor operatedcables coupled to various links that form guide 2, as is known in theart (see e.g., U.S. Pat. No. 3,060,972 (filed 22 Aug. 1957), whichillustrates basic cable steering principles, and which is incorporatedherein by reference. Other steering mechanisms may include the use ofshape memory alloy (e.g., Nitinol), electroactive polymers (“artificialmuscle”), components positioned by externally generated magnetic forces,and the like. Examples of known steerable guides in the medical devicefield are steerable endoscopes and catheters. Steerable, flexiblestructures are further illustrated by U.S. Pat. No. 5,251,611 (filed 7May 1991), which is incorporated by reference.

The term “flexible” includes devices that have many short pivotallycoupled links that function as “vertebrae”, which is how many commercialendoscopes are constructed, and also devices that are continuouslycurving, such as a bendable rubber tube.

In some instances guide 2 itself may be transitioned between arelatively lesser stiffness (flexible) to a relatively higher stiffness(effectively rigid). Such a transition between flexible and rigid statesmay be done by, e.g., increasing friction between jointed elements byapplying tension to cables, or by holding an activation mechanism (e.g.,hand wheel, servomotor) in place. Servomotors may be mechanicallystabilized, e.g., by “braking” or “clutching”, or they may be stabilizedusing software control.

In order to provide additional stiffness to guide 2, in accordance withaspects of the invention longitudinal beams 14 are positioned around theoutside of the guide as shown in FIG. 1. Various longitudinal beamarrangements and configurations are described in detail below. Thearrangement of longitudinal beams is a stiffening assembly 16. Twelvebeams 14 are shown arranged around guide 2 in FIG. 1, which isillustrative of various numbers that may be used. Beams 14 arepositioned so that an inner face is adjacent the outer surface of guide2, and so that they are each in sliding contact with one another.Consequently, as guide 2 bends along longitudinal axis 8, the individualbeams 14 bend and slide with reference to one another. This feature isillustrated in FIG. 2A, which is a diagrammatic plan view of thesurrounding longitudinal beams 14 bending and sliding against oneanother as guide 2 bends along its longitudinal axis. FIG. 2A showsbeams 14 as stationary with reference to each other at roughly half-waybetween proximal and distal ends, and it can be appreciated that such astationary relationship can be at the proximal or distal ends, anyposition between the proximal or distal ends, or at no particularposition between the proximal and distal ends. When the beams slide inrelation to one another, stiffening assembly 16 is in a flexible state.

In accordance with an aspect of the invention, stiffening mechanism 16is placed in a stiffened state by compressing the longitudinal beams 14against each other in a circumferential direction so that frictionbetween the beams effectively prevents the beams from sliding againstone another. Accordingly, a mechanical shear force experienced on oneside of stiffening assembly 16 is transferred through adjacent, clampedlongitudinal beams to the opposite side of the stiffening mechanism. Forexample, once endoscope 2 is bent as shown in FIG. 2A, with stiffeningassembly 16 in a flexible state, then stiffening assembly 16 is placedin a stiffened state by clamping the longitudinal beams against oneanother. The result is that a shear force, e.g., in an outer bend radiusbeam 14 a, shown as arrow 18, is transferred to an inner bend radiusbeam 14 b by the intervening clamped beams. Consequently, the portion ofguide 2 that is covered by stiffening assembly 16 is stiffened, or it isfurther stiffened if guide 2 has its own stiffening mechanism. Variousways of clamping the beams are described below. When stiffening assembly16 is unclamped it returns to a flexible state in which the longitudinalbeams slide relative to one another, and the portion of guide 2 that iscovered by stiffening assembly 16 is once again bendable. Of course,stiffening assembly 16 may provide stiffness when guide 2 issubstantially straight as well.

An advantage of stiffening a guide tube/endoscope during surgery is thatthe increased stiffness is used to counteract the reactive forces on oneor more instruments that extend through the guide tube/endoscope. Forexample, if an instrument that extends through the guide tube/endoscopegrasps and pulls tissue, the instrument tends to pull the supportingguide tube/endoscope towards the tissue, thus reducing the effectivenessof the instrument. And, if the instrument suddenly releases the tissue,the guide tube/endoscope tends to snap back to its original position.Stiffening the guide tube/endoscope helps to resist such reactive forcesand provides a stable platform for surgical instruments, which makes theinstruments more effective during work at the surgical site. Thisstiffening feature may allow the distal portion of the guide to becantilevered, thus eliminating the need to brace the distal end of theguide against hard or soft tissue.

FIG. 2B is another diagrammatic plan view of the longitudinal beamsbending and sliding with reference to one another as the guide bendsalong its longitudinal axis. In the FIG. 2B depiction, the longitudinalbeams 14 of the stiffening assembly 16 surround a compound curve in theguide 2. This compound curve illustrates that the stiffening assemblymay be configured to accommodate multiple two- or three-dimensionalcurves in the guide. As shown in FIG. 2B, the longitudinal beams areheld stationary with reference to one another at approximately amid-point between the proximal and distal ends of the beams. In otherimplementations the beams may be held stationary with reference to oneanother at other locations along the length of the stiffening assembly.The beams may be held stationary at a particular location by, e.g.,anchoring them to the guide. Alternatively, the beams may not beanchored with reference to a particular location along the length of theguide, and instead they can be generally constrained to maintain asliding relationship along a significant portion of their lengths.

FIG. 3 is an exploded perspective diagrammatic view of bendablelongitudinal beams 14 in a stiffening mechanism 6. As shown in FIG. 3,the longitudinal beams 14 are positioned lengthwise around longitudinalaxis 8 so as to generally form a tube arrangement. Each longitudinalbeam 14 has an inner surface 20 closest to the longitudinal axis 8, anouter surface 22 farthest from the longitudinal axis 8, and two lateralsurfaces 24 between inner surface 20 and outer surface 22. As the beams14 are compressed radially inward towards the longitudinal axis, thesurfaces 24 contact each other, and friction between surfaces 24 keepsadjacent beams from moving in relation to one another.

FIGS. 4A-4F are diagrammatic cross-sectional end views that illustratevarious cross sectional shapes of the beams themselves and arrangementsof the beams around the longitudinal axis 8. As shown in FIG. 4A, insome aspects each longitudinal beam 14 has a substantially rectangularcross section (squares are illustrated).

As shown in FIG. 4B, in some aspects each longitudinal beam 14 issubstantially rectangular, and the lateral surfaces 24 are angled sothat they contact each other along the full surface of the face. (Theillustrated cross-sectional shape is a trapezoid.) This anglingincreases the lateral surface 24 contact area between adjacent beams,which can result in increased shear transfer capability. FIG. 4B is alsoillustrative of beams that have an arcuate cross section in thecircumferential direction (i.e., either one or both of inner and outerfaces 20,22 are curved) so that the lateral surfaces 24 abut oneanother.

In yet other aspects, each longitudinal beam 14 has a substantiallycircular cross section as shown in FIG. 4C. A longitudinal beam 14 witha circular cross section can also be considered to have inner, outer,and lateral surfaces 20,22,24, even though such surfaces are not flat.One advantage of such a circular cross section is that larger beams 14are not subject to instability and non-uniform or asymmetricaldeformation that tends to occur when, for instance, an element with anon-round or non-square cross-sectional shape is bent.

FIG. 4D illustrates that the longitudinal beams 14 are not alwaysequidistant from the longitudinal axis 8. For example, beams 14 may bearranged in a roughly elliptical (as shown), oval, or other geometric(e.g., polygonal) cross-sectional shape around the longitudinal axis.FIG. 4D further illustrates that longitudinal beams 14 may be arrangedsuch that the tube structure is more flexible in one plane (e.g., pitch;up and down as shown in the drawing) than in another plane (e.g., yaw;left and right as shown in the drawing). Likewise, if the longitudinalbeams 14 are arranged in roughly a square cross-sectional pattern, thestiffness of the tube structure will be generally the same for pitch andyaw, but the tube structure will be stiffer for bends out of the pitchor yaw planes.

FIG. 4E illustrates that the longitudinal beams may be arranged in twoor more layers around the longitudinal axis. Accordingly, in a stiffenedstate shear force is transferred between beams in inner and outerlayers, as well as between beams in the same layer. It can beappreciated that FIG. 4E illustrates that each beam 14 may be a smallwire or filament, and that such small beams may be loosely packed arounda guide, as illustrated in FIG. 4F, so that they frictionally engageeach other when compressed together to provide stiffening. For example,one or more layers of 0.010-inch diameter carbon rods may be used.

An internal support structure may be necessary in order to prevent thetube-like structure of the stiffening assembly from collapsing under abending load (e.g., due to increasing ovalization until a maximumbending moment capacity is reached). In some implementations the guide 2may provide sufficient support. In other implementations, anintermittent series of inner rings or bulkheads can be used. Or, ahelical wound coil may be used to provide continuous internal support.These structures are illustrative of various internal support structuresthat may be used to prevent the stiffening assembly from collapsing asits radius of curvature decreases.

B. Laminar Construction

In a further aspect of the invention, each longitudinal beam 14 may bemade of two or more longitudinal laminar elements (laminae). FIGS. 5A-5Care diagrammatic cross-sectional end views of various laminarlongitudinal beams 14.

As shown in FIG. 5A, longitudinal beam 14 is made of several planarlaminae 30 stacked on one another in a radial direction. Each lamina 30has an inner (towards the tube's centerline; longitudinal axis) surface32, an outer (away from the tube's centerline; longitudinal axis)surface 34, and two lateral surfaces 36. Example dimensions are0.040-inch wide and 0.010-inch thick. The laminae 30 are not permanentlyfixed to one another, so that as longitudinal beam 14 bends in aflexible state, the laminae 30 slide in relation to one another.Accordingly, when the laminae 30 are allowed to slide, the laminarlongitudinal beam 14 as illustrated in FIG. 5A has a pitch stiffnessthat is less than a similarly sized monolithic longitudinal beam made ofsubstantially the same material.

FIG. 5B shows that the laminae 30 may be arranged in a circumferentialdirection, or that laminae stacked in a radial direction may besubdivided in a circumferential direction. As shown, the laminae 30 eachhave a generally square cross section and are arranged in a 4×8 (thenumbers and shapes are merely illustrative) matrix so that longitudinalbeam 14 has a generally rectangular cross section. Again, each lamina 30may slide in relation to the others so that longitudinal beam 14'sstiffness is reduced in more than one plane. Such an arrangement helpsreduce or eliminate the tendency of a rectangular cross-sectional beamto twist as it is bent in the plane of its long side, because thelateral surfaces 36 of the laminae 30 may slide against each other.Reference is made again to FIGS. 4E and 4F, which also illustrate thenotion of many small laminar beams forming a larger beam, and that theindividual laminae may have circular or other rounded cross-sectionalshapes.

FIG. 5C illustrates that the laminae 30 may have cross sections thatinterlock to further control twisting as longitudinal beam 14 bends invarious directions. As shown in FIG. 5C, the cross sections of thelaminae 30 are generally trapezoidal so that the lateral surfaces 36 ofeach lamina are angled against each other. Consequently, the laminae 30generally engage two or more adjacent laminae 30 as longitudinal beam 14bends in various directions. Example dimensions: the laminae areapproximately 0.025-inch wide, approximately 0.005-inch thick, and thelateral surfaces are angled at approximately 45 degrees.

FIGS. 6A-6D are diagrammatic side views of various illustrative laminarlongitudinal beam 14 configurations. As shown in FIG. 6A, the laminae 30are substantially the same thickness, and each one extends for thelength of longitudinal beam 14. In FIG. 6B, the laminae 30 aresubstantially the same length, but each lamina has a differentthickness. As shown, laminae 30 a-30 d become progressively thickertowards the longitudinal axis 8 (not shown). Example dimensions: lamina30 a is 0.001-inch thick, 30 b is 0.002-inches thick, 30 c is0.003-inches thick, and 30 d is 0.004-inches thick. Top, bottom, ormiddle laminae may be thicker than the others, depending on desiredlongitudinal beam stiffness qualities.

FIGS. 6C and 6D illustrate that the longitudinal beams may be configuredto have varying stiffness along their length. In one case, monolithiclongitudinal beams may be tapered from one end to another so that thebeam stiffness at the relatively thinner end is less than the beamstiffness at the relatively thicker end. Alternatively, as illustratedby FIGS. 6C and 6D, the length of the laminae 30 may be varied to varythe stiffness along the length of a beam 14. FIG. 6C shows progressivelylonger laminae 30 e-30 h so that longitudinal beam 14 becomesprogressively less stiff as it becomes made of fewer laminae. FIG. 6Dillustrates a similar configuration, except that the thickness of theprogressively longer laminae 30 i-30 m varies so that the stiffness ofbeam 14 can be configured as desired. Skilled artisans will understandthat longitudinal beam 14 stiffness may increase from distal to proximalends, and vice-versa. And, the lengths of individual laminae may bevaried in the circumferential direction so that laminae at one lateralside of the beam or at a middle location are longer that laminae at theopposite lateral side of the beam.

The cross section of the individual beams or laminae must be smallenough to permit a desired minimum bend radius without exceeding theyield strength of the beam material. The use of two or more layers oflongitudinal beams, as illustrated by FIGS. 4E and 4F, may serve toallow the stiffening assembly to be bent in a smaller bend radius and/orbent with less force while in the flexible state, without reducing itsstiffness in the stiffened state.

C. Clamping

As described above, the longitudinal beams of the stiffening assemblyare bendable and slide in relation to one another. Once the stiffeningassembly is bent into a desired configuration, the beams and/or laminaeare clamped against one another and/or against a support structure(e.g., a bulkhead) in order to stiffen the assembly.

Accordingly, it is desirable that the longitudinal beams and laminae bea high strength, high modulus of elasticity material, such ashigh-strength steel or super alloy, or a carbon/epoxy composite. It mayalso be desirable to use materials or surface coatings for the beams andlaminae that achieve a relatively large static coefficient of frictionwhen clamped and a relatively low dynamic coefficient of friction whenunclamped. If materials or coatings are chosen such that the coefficientof static friction is significantly higher than the dynamic coefficientof friction at low speeds, then the stiffening assembly will have anextremely high stiffness in a stiffened state when clamped along thelength of a longitudinal beam (e.g., using a vacuum, as described below)and a relatively low resistance to bending in a non-stiffened state whenclamping is released.

As described above, clamping the surfaces of individual beams againstone another transfers shear forces from one side of the stiffeningassembly to the other to stiffen the assembly, and clamping laminaetogether transfers shear forces within a beam to stiffen the beam. Sincethe stiffness of a beam in bending is proportional the cube of itsthickness parallel to the direction of the applied bending force, aclamped laminar beam may have a bending stiffness 100 times larger—ormore—than when unclamped. The stiffness increase depends on the beamdimensions, and to some extent the laminar configuration of the beamswhen applicable, as well as on the clamping force and area clamped.

In accordance with an aspect of the invention, a vacuum is used to clampmonolithic or laminar beams together in order to accomplish sheartransfer along the length of the beam, or along a significant portion ofthe length. The vacuum can also be used to clamp laminae in individualbeams together to stiffen the beams.

FIG. 7A is a diagrammatic cross-sectional view that shows longitudinalbeams 14 arranged in a stiffening assembly 16 around longitudinal axis8. The longitudinal beams 14 are positioned between an inner wall 40 andan outer wall 42. In one aspect the longitudinal beams 14 free floatbetween the inner and outer walls 40,42. The inner and outer walls 40,42are flexible so that the stiffening assembly may bend. A vacuumintroduced in the space 44 between the walls causes the longitudinalbeams 14 to be clamped between the walls, thereby stiffening theassembly in its current curved configuration. If applicable, theintroduced vacuum also causes the walls to clamp the laminae in thebeams. In one aspect, inner wall 40 is the outer surface of the guide 2(FIGS. 1 and 2A-2B), such as the outer surface of a flexible, steerableendoscope. It can be appreciated that depending on variousconfigurations, a vacuum between the walls may cause a compression forceradially inwards towards the longitudinal axis, radially outwards awayfrom the longitudinal axis, or both.

In some aspects the space 44 between the inner and outer walls is filledwith a gas in the unclamped (non-stiffened) state, which is evacuated inthe clamped (stiffened) state. In other aspects, space 44 may be filledwith a liquid 45. Referring to the top detail view in FIG. 7A, duringthe unclamped state, a thin film 46 of the liquid acts as a lubricantbetween beams 14 and/or laminae 30. This thin film facilitates bendingby providing hydrodynamic lubrication between surfaces of the beams andlaminae, which greatly reduces dynamic friction between the slidingsurfaces. Referring to the bottom detail view in FIG. 7A, during theclamped state the liquid is effectively evacuated, and the surfaces ofthe beams and laminae contact one another. The contact results inboundary lubrication between contacting surfaces with a correspondinghigher coefficient of friction, thus greatly stiffening the assembly.The introduction and evacuation of a lubricating fluid between thesliding surfaces allows both the “stick” and “slip” characteristics ofthe mechanical stick-slip phenomenon to be used to advantage in thestiffening mechanism.

For use in a surgical device, the liquid may be a biocompatiblelubricant, e.g., water, alcohol, or a fluid as described in U.S. Pat.No. 7,060,199 B2 (filed 22 Dec. 2004), which is incorporated herein byreference. Water is effective because of its relatively low surfacetension and ease of effectively complete evacuation; alcohol, even moreso. One or both opposing surfaces of the walls may have protrusions orother structures (e.g., ribs, channels, and the like) that facilitatecomplete evacuation of the gas or liquid from space 44. In some aspects,the protrusions or other structures may assist holding the beams and/orlaminae in place between the inner and outer walls.

FIGS. 7B and 7C are diagrammatic cross sectional detail views of anotherimplementation of hydrodynamic lubrication. As shown in FIG. 7B, alubricating fluid 47 is introduced between longitudinal filaments 48,which are illustrative of beams or laminae. This lubricating fluid helpsto displace the walls 42 and 44 apart, providing room for the filamentsto separate, and it provides a hydrodynamic lubrication between thefilaments when the stiffening assembly is in an unclamped, flexiblestate. As shown in FIG. 7C, the fluid is effectively removed so that thefilaments contact one another, and when a clamping force is appliedradially to the longitudinal filaments, the stiffening assembly isplaced in a clamped, stiffened state.

FIG. 8 is a schematic view of a vacuum clamping system for a minimallyinvasive surgical assembly 50. As shown in FIG. 8, a minimally invasivesurgical instrument 52 extends through guide 2. Guide 2 helps guideinstrument 52 towards a surgical site within a patient. In oneillustrative aspect, guide 2 has an outside diameter on the order of15-18 mm. Either guide 2 or instrument 52, or both, may be an endoscope.Surgical instruments extending through an endoscope or guide tube arefurther illustrated by U.S. Patent Application Pub. No. US 2008/0065105A1 (filed 13 Jun. 2007), which is incorporated by reference. Theassembly represented by FIG. 8 is illustrative of a generalconfiguration using other clamping implementations as well.

As depicted in FIG. 8, a vacuum-operated stiffening assembly 16 ispositioned around a distal portion of guide 2. As described above,vacuum source 54 evacuates space 44 to clamp longitudinal beams 14.Optional pressure source 53 provides gas or liquid insufflation, asdescribed above, when the stiffening assembly is in its unclamped,flexible state. Introducing the lubricating liquid under pressure helpsform the lubricating film between sliding surfaces. Vacuum source 54provides, e.g., 10 psi of vacuum, which is available from typicalcommercially available vacuum sources. Vacuum source 54 is used toeffectively evacuate the gas or liquid and bring the sliding surfacesinto contact with one another.

During a surgical procedure, the guide 2 is introduced into the patientand is steered towards a surgical site 55 (e.g., in the abdomen orthorax). Once the distal end of the guide is positioned in a workingposition and orientation at the surgical site, the stiffening assembly16 is used to stiffen the guide to maintain the desired position andorientation. When the distal portion of guide is stiffened by stiffeningassembly, the distal portion provides a stable, cantilever platform forinstrument 52 to work at the surgical site. This platform is stableagainst tissue reactive forces against end effector 56 during a surgicalprocedure. End effector 56 is illustrative of, e.g., graspers, needledrivers, scissors, retractors, electrocautery electrodes, and the like.

An advantage of using a vacuum to clamp the longitudinal beams is thatthe vacuum may be quickly released by venting the evacuated space to thesurrounding ambient atmosphere. Or, the space between the clamping wallsmay be insufflated with a small positive pressure to help the beams andthe laminae freely slide when the flexible tube is repositioned.

FIG. 8 also illustrates that one or more microvalves may be used to aidinsufflation and evacuation of fluid in the vacuum clamping stiffeningassembly. As shown in FIG. 8, an illustrative microvalve 57 ispositioned at or near the distal end of the stiffening assembly. Themicrovalve assembly may contain a sensor that senses the presence of afluid. During insufflation, the microvalve at the distal end is openedto allow any ambient gas (e.g., air) in the stiffening assembly toescape as, e.g., a liquid is introduced into the proximal end of thestiffening assembly by pressure source 53. If a sensor is used, then thesensor can generate a signal to close the microvalve when the sensordetects the insufflation fluid. Alternatively, the microvalve may beclosed in accordance with another parameter, such as elapsedinsufflation time. During evacuation, the microvalve may be opened toallow ambient air to enter the stiffening assembly, thus assistingevacuation of the liquid. The operation of the pressure source, thevacuum source, and the microvalve may be coordinated by an electroniccontroller 58 (e.g., microprocessor-based). The controller may operateeach component separately.

Although vacuum clamping has some noteworthy characteristics, otherclamping methods may be used. In some aspects, discussed below, thelongitudinal beams may not contact each other when the stiffeningassembly is in a stiffened state. In this situation, shear force fromone beam is transferred to another beam via an intermediate structure.For example, shear forces may be transferred from one side of astiffening assembly via bulkheads rather than directly between adjacentlongitudinal beams.

FIG. 9 is a diagrammatic perspective view of another aspect of astiffenable assembly 16 in accordance with the invention. Twoillustrative annular support bulkheads 60 are shown. Each bulkhead 60has a number of holes 62 arranged to allow longitudinal beams 14 to passthrough. Only a single longitudinal beam 14 is shown so that thebulkheads may be seen with more clarity, and it should be understoodthat longitudinal beams 14 extend though all holes 62. In some instancesholes 62 are generally shaped to allow a close and sliding fit forlongitudinal beams 14. And, if longitudinal beams 14 are made ofindividual laminae, as described above, then the individual laminae mayslide with reference to one another as the assembly bends. In otherinstances, longitudinal beams 14 may be anchored (e.g., glued, welded,friction fit, etc.) within holes 62 of one bulkhead so that neither theynor their laminae slide. Bulkheads 60 are also shown having a largecentral hole 64, which is illustrative of various numbers of other suchholes that may allow passage of, e.g., guide 2, or other surgicaldevice, or control cables for distal surgical instrument end effectors.

FIG. 9 also shows a clamping mechanism 66 that is used to clamp thebeams 14 against the bulkheads 60 and to clamp the laminae 30 againstone another. As shown in FIG. 9, one implementation of clampingmechanism 66 is a split ring that may be radially expanded to compresseach longitudinal beam 14 against the outer surfaces of the holes 62 inbulkhead 60. This split ring is illustrative of various mechanisms andmechanical configurations that may be used to clamp the beams.

FIG. 10A is a diagrammatic cross-sectional view that illustrates oneaspect of clamping mechanism 66. As shown in FIG. 10A, an activatingcable 68 (or rod, or other suitable mechanical linkage) passes throughbulkhead 60 and is connected to wedge 70 by the use of a swaged/crimpedfitting 72 or other suitable way. When tension is applied to cable 68,the inclined surface of wedge 70 engages clamping mechanism 66 andforces it outward, thus compressing beam 14 and laminae 30 againstbulkhead 60. Wedge 70 is illustrative of both a single chamfered ringthat generally concentrically engages clamping mechanism 66, and ofnumerous single wedges that engage clamping mechanism 66 near each hole62 in bulkhead 60. FIG. 10A shows clamping mechanism 66 compressing beam14 and laminae 30 outwards, away from the center of the stiffeningassembly 16, but it can be seen that the configuration can be easilymodified to compress the beams and laminae radially inwards.

FIGS. 10B-10D are diagrammatic cross-sectional views that illustrateother aspects and implementations of clamping mechanisms. As shown inFIG. 10B, cable 74 passes through wedge structure 76 and is connected toclamping mechanism 78. As tension is applied to cable 74, clampingmechanism 78 is drawn towards wedge structure 76, which forces clampingmechanism 78 against longitudinal beam 14 and compresses beam 14 andlaminae 30 against bulkhead 60. In some aspects wedge structure 76 ispart of bulkhead 60. In other aspects, wedge structure 76 may beattached to (or be an integral part of) the lamina 30 against whichclamping mechanism 78 presses.

FIG. 10C illustrates another aspect of activating a clamping mechanism.As shown, cable 80 is routed from the inside to the outside (or viceversa) of bulkhead 60 to engage clamping mechanism 78. Cable 80 entersbulkhead 60 though a passage, passes over, e.g., a pulley or a fairlead(either of the two may be used, with consideration being given tofriction) to extend outward, and then passes over another pulley orfairlead in wedge structure 76 to engage clamping mechanism 78. Pulley82 and fairlead 84 as shown in FIG. 7B are illustrative of thepositioning of such cable routing components.

FIG. 10D illustrates yet another aspect of activating a clampingmechanism. As shown in FIG. 10D, cable 86 inserts into bulkhead 60,passes over pulley 88 (or a fairlead or other guiding structure), andextends radially outward to engage clamping mechanism 90. When tensionis applied to cable 86, clamping mechanism 90 is pulled inward againstlongitudinal beam 14, which compresses beam 14 and laminae 30 againstbulkhead 60.

It can be seen from the various aspects illustrated by FIGS. 10A-10D,that there are many possible ways of applying a force either radiallyinwards or outwards to clamp the beams to a bulkhead and to compress thelaminae against each other, thereby enabling shear transfer to increasethe stiffness of the stiffening apparatus. Other clamping mechanisms mayinclude, e.g., the use of a shape memory alloy (SMA) that when heated(e.g., by use of an electrical current) expands to change a clampingstate of the longitudinal beams (i.e., either the clamped or unclampedstate exists when the SMA is heated, depending on the designconfiguration).

FIG. 11 is a diagrammatic view that illustrates another implementationof a stiffening assembly 16 in accordance with aspects of the invention.FIG. 11 depicts a stiffening assembly, as generally described withreference to FIG. 9, positioned around a distal portion of a steerable,bendable guide 2. FIG. 11 depicts a configuration in which fourlongitudinal beams 14 are equidistantly spaced around guide 2 (one beamis hidden from view behind the guide). This configuration isillustrative of various configurations in which two, three, or more(e.g., 12) longitudinal beams are used. A large number of longitudinalbeams is not shown in the figure so that the principles of variousaspects of the invention can be clearly seen.

Bulkhead 60 a is coupled to guide 2 near its distal end 6. The distalends of longitudinal beams 14 are anchored in bulkhead 60 a. A secondbulkhead 60 b is coupled to guide 2 at a location proximal of bulkhead60 a. The two bulkheads 60 shown in FIG. 11 are illustrative of variousnumbers of bulkheads that may be used to guide and support, andoptionally clamp, the longitudinal beams.

As the distal part of guide 2 bends, e.g., to the right as depicted inFIG. 11, longitudinal beams 14 slide through holes in bulkhead 60 b asdescribed above. Thus the longitudinal beam at the inside of the guide'sbend slides proximally through bulkhead 60 b, as shown by arrow 100 a.Similarly, the longitudinal beam at the outside of the guide's bendslides distally through bulkhead 60 b, as shown by arrow 100 b. Inaddition, the individual laminae of the longitudinal beams at the insideand outside of the guide's bend slide against one another. The laminaefarthest from the guide's central longitudinal axis slide the farthest,as shown by arrows 102 a (inner curve) and 102 b (outer curve). Whenguide 2 is at a desired bend angle, then clamping mechanism 66 isactuated as described above (components such as cables are omitted fromthe drawing for clarity) to clamp the beams against the bulkhead and thelaminae against one another. Accordingly, when the stiffening mechanismis clamped, lateral forces acting on the guide's distal end cause shearforces within one or more longitudinal beams, and these shear forces aretransferred from the beam, through the bulkhead(s), to one or more beamson the opposite side of the guide.

FIG. 11 shows only the distal end of guide 2, but it can be appreciatedthat with longer longitudinal beams and more bulkheads, various lengthsof the guide can be stiffened by using a stiffening assembly inaccordance with aspects described herein. Further, by actuatingdifferent clamping implementations at various bulkheads, one or moreportions of the guide may be stiffened while one or more other portionsremain flexible. For example, in a three-bulkhead arrangement, if thelongitudinal beams are held stationary with reference to the middlebulkhead, then the proximal section of the guide bounded by the mostproximal and middle bulkheads may be stiffened by clamping at theproximal bulkhead. Similarly, the distal section bounded by the middleand most distal bulkheads can be stiffened by clamping at the distalbulkhead. And, with reference to FIGS. 6C and 6D above, it can beappreciated that by varying the laminar composition of the longitudinalbeams, various stiffnesses can be applied to various parts of the guide.It can be seen that using separate stiffening assemblies for two or moreportions of the guide may be implemented with vacuum clamping, as wellas various other ways to clamp the beams and laminae.

A flexible sheath may be placed over the stiffening assembly to preventtissue damage as the guide moves within a patient or to prevent bodyfluids and tissue from entering the stiffening assembly.

The longitudinal beam clamping described with reference to FIGS. 9-11occurs over a relatively small proportion of the beam. The stiffness ofthe stiffening assembly is dependent on the amount of shear transferthat can occur between beams, and the stiffness of a laminar beam isdependent on the amount of friction and clamping force that can begenerated between the laminae. It can be seen that a vacuum clampingmechanism, such as illustrated in FIG. 8, may provide relatively higherinter-beam and inter-lamina shear transfer, and thus more assembly andbeam stiffness, than the clamping mechanism illustrated in FIGS.10A-10D, because it creates clamping force over a larger area betweenbeams and laminae. Accordingly, in general, the larger the clamping areaon the longitudinal beam, the stiffer the beam.

It can be seen that a stiffenable assembly in accordance with aspects ofthe invention may have significant benefits to minimally invasivesurgery, and particularly to telerobotic surgery done in the manner ofthe da Vinci® Surgical System, manufactured by Intuitive Surgical,Sunnyvale, Calif. Aspects may be used to stiffen and hold a guide tubein a fixed shape to provide a platform against tissue reactive forcesfrom surgical instruments that are supported by the guide.

I claim:
 1. A stiffening assembly comprising: a flexible tube comprisinga plurality of longitudinal sections positioned lengthwise around alongitudinal axis, the flexible tube configured to transition between asliding state wherein the longitudinal sections slide longitudinallyrelative to one another and a clamped state wherein the longitudinalsections are clamped in a substantially fixed position relative to oneanother.
 2. The stiffening assembly of claim 1 wherein each of thelongitudinal sections has an arcuate cross-section.
 3. The stiffeningassembly of claim 1 wherein each of the longitudinal sections has atrapezoid shape cross-section.
 4. The stiffening assembly of claim 1wherein each of the longitudinal sections has a rectangular crosssection.
 5. The stiffening assembly of claim 1 wherein each of thelongitudinal sections has at least one curved surface.
 6. The stiffeningassembly of claim 1 wherein in the clamped state, each of thelongitudinal sections contacts an adjacent one of the plurality oflongitudinal sections along an entire length of the adjacent one of theplurality of longitudinal sections.
 7. The stiffening assembly of claim1: wherein in the clamped state the beams are clamped against oneanother.
 8. The stiffening assembly of claim 1: wherein in the clampedstate the beams are clamped against a bulkhead.
 9. The stiffeningassembly of claim 1: wherein at least one of the plurality oflongitudinal sections is comprised of a plurality of longitudinallaminar elements.
 10. The stiffening assembly of claim 9: whereinlengths of the laminar elements are different from one another.
 11. Thestiffening assembly of claim 9: wherein thicknesses of the laminarelements are different from one another.
 12. The stiffening assembly ofclaim 9: wherein the plurality of laminar elements comprises a pluralityof filaments.
 13. The stiffening assembly of claim 1 further comprisinga clamping mechanism configured to transition the longitudinal sectionsbetween the sliding and clamped states.
 14. The stiffening assembly ofclaim 13: wherein the a clamping mechanism comprising a vacuum source.15. The stiffening assembly of claim 13: wherein the clamping mechanismapplies force radially outward from the longitudinal axis.
 16. Thestiffening assembly of claim 13: wherein the clamping mechanism appliesforce radially inward from the longitudinal axis.
 17. The stiffeningassembly of claim 1 further comprising: a support structure positionedto prevent collapse of the flexible tube when the stiffening assembly issubjected to a bending load.
 18. A method of stiffening a flexible tubecomprising: inducing a first state in which a plurality of longitudinalsections of the flexible tube are positioned lengthwise around alongitudinal axis and clamped in a substantially fixed position relativeto one another and inducing a second state in which the longitudinalsections slide longitudinally relative to one another.
 19. The method ofclaim 18 wherein in the first state, each of the longitudinal sectionscontacts an adjacent one of the plurality of longitudinal sections alongan entire length of the adjacent one of the plurality of longitudinalsections.
 20. The method of claim 18 wherein each of the longitudinalsections has an arcuate cross-section.